In the course of completing an oil and/or gas well, a string of protective casing can be run into the wellbore followed by production tubing inside the casing. The casing can be perforated across one or more production zones to allow production fluids to enter the casing bore. During production of the formation fluid, formation sand may be swept into the flow path. The formation sand tends to be relatively fine and can erode production components in the flow path. In some completions, the wellbore is uncased, and an open face is established across the oil or gas bearing zone. Such open wellbore (uncased) arrangements are typically utilized, for example, in water wells, test wells, and horizontal well completions.
When formation sand is expected to be encountered, one or more sand screens can be installed in the flow path between the production tubing and the perforated casing (cased) and/or the open wellbore face (uncased). A packer is customarily set above the sand screen to seal off the annulus in the zone where production fluids flow into the production tubing. The annulus around the screen can then be packed with a relatively coarse sand (or gravel) which acts as a filter to reduce the amount of fine formation sand reaching the screen. The packing sand is pumped down the work string in a slurry of water and/or gel and fills the annulus between the sand screen and the well casing/reservoir. In well installations in which the screen is suspended in an uncased open bore, the sand or gravel pack may serve to support the surrounding unconsolidated formation.
During the sand packing process, annular sand “bridges” can form around the sand screen assembly that may prevent the complete circumscribing of the screen structure with packing sand in the completed well. This incomplete screen structure coverage by the packing sand may leave an axial portion of the sand screen exposed to the fine formation sand, thereby undesirably lowering the overall filtering efficiency of the sand screen structure.
One conventional approach to overcoming this packing sand bridging problem has been to provide each generally tubular filter section with a series of shunt tubes that longitudinally extend through the filter section. In the assembled sand screen structure, the shunt tube series forms a flow path extending along the entire length of the sand screen structure. The flow path operates to permit the inflowing packing sand/gel slurry to bypass any sand bridges that may be formed and permit the slurry to enter the annulus between the casing/reservoir beneath a sand bridge, thereby forming the desired sand pack beneath it.